U.S. patent application number 15/407969 was filed with the patent office on 2017-05-04 for communication terminal.
The applicant listed for this patent is Sun Patent Trust. Invention is credited to Takahisa Aoyama, Jun Hirano, Takashi Tamura.
Application Number | 20170126373 15/407969 |
Document ID | / |
Family ID | 43386252 |
Filed Date | 2017-05-04 |
United States Patent
Application |
20170126373 |
Kind Code |
A1 |
Aoyama; Takahisa ; et
al. |
May 4, 2017 |
COMMUNICATION TERMINAL
Abstract
A communication terminal is capable of simultaneously
communicating through a plurality of carriers by carrier
aggregation, and the communication terminal comprises: a quality
measurement unit for measuring the reception quality of a radio
wave transmitted through a plurality of carriers from a base
station of a connected cell to obtain a measured value; a primary
carrier storage unit storing information specifying a primary
carrier chosen from the plurality of carriers; a comparator for
comparing a measured value of the primary carrier measured by the
quality measurement unit to a threshold value; and a cell search
unit for searching for another cell when the measured value of the
primary carrier is less than or equal to the threshold value.
Consequently, a search threshold value for carrier aggregation can
be appropriately determined to perform a cell search and a quality
measurement.
Inventors: |
Aoyama; Takahisa; (Kanagawa,
JP) ; Hirano; Jun; (Kanagawa, JP) ; Tamura;
Takashi; (Kanagawa, JP) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Sun Patent Trust |
New York |
NY |
US |
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Family ID: |
43386252 |
Appl. No.: |
15/407969 |
Filed: |
January 17, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13379471 |
Dec 20, 2011 |
9596631 |
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PCT/JP2010/003501 |
May 25, 2010 |
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15407969 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 47/29 20130101;
H04L 5/0091 20130101; H04W 36/0083 20130101; H04W 28/0236 20130101;
H04L 5/001 20130101; H04W 24/10 20130101; H04W 36/00835 20180801;
H04L 5/0053 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04L 12/801 20060101 H04L012/801; H04W 36/00 20060101
H04W036/00; H04W 28/02 20060101 H04W028/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2009 |
JP |
2009-147778 |
Claims
1. A communication terminal, comprising: communication circuitry
which, in operation, communicates with a first base station through
a plurality of carriers, including at least a primary carrier and a
secondary carrier, by carrier aggregation; and control circuitry,
which, in operation: measures reception quality of radio waves
transmitted through the plurality of carriers from the first base
station to obtain measured values; compares the measured value of
the primary carrier to a first threshold value; and compares the
measured value of the secondary carrier to a second threshold
value, wherein the control circuitry: when periods during which the
communication terminal receives data discontinuously are
configured: when the measured value of the primary carrier is lower
than the first threshold value, performs a cell search for a first
corresponding carrier having a same frequency as the primary
carrier, of a first neighboring cell, and for a second
corresponding carrier, having a same frequency as the secondary
carrier, of a second neighboring cell; and when the measured value
of the primary carrier is equal to or higher than the first
threshold value, does not perform the cell search; and when the
periods are not configured, determines whether to perform the cell
search based on the measured value of the primary carrier and the
measured value of the secondary carrier.
2. The communication terminal according to claim 1, wherein the
communication terminal is connected to a serving primary cell
through the primary carrier and is connected to a serving secondary
cell through the secondary carrier, wherein the serving primary and
secondary cells are supported by the first base station.
3. The communication terminal according to claim 2 wherein the
first neighboring cell is different from the serving primary cell
and the second neighboring cell is different from the serving
secondary cell, wherein the first and second neighboring cells are
target cells for the communication terminal to connect to through
the first and second corresponding carriers and are supported by a
second base station different from the first base station, and the
control circuitry, in operation, measures the reception quality of
radio signals transmitted through the first and second
corresponding carriers of the first and second neighboring
cells.
4. The communication terminal according to claim 1, wherein the
primary carrier is a backward compatible component carrier and the
secondary carrier is a non-backward compatible component
carrier.
5. The communication terminal according to claim 1, wherein the
primary carrier is set by the first base station.
6. The communication terminal according to claim 1, wherein the
primary carrier is set by the communication terminal.
7. A method performed by a communication terminal, the method
comprising: controlling communication with a first base station
through a plurality of carriers including at least a primary
carrier and a secondary carrier by carrier aggregation, measuring
the reception quality of radio waves transmitted through the
plurality of carriers from the first base station to obtain
measured values; comparing the measured value of the primary
carrier to a first threshold value; comparing the measured value of
the secondary carrier to a second threshold value; when periods
during which the communication terminal receives data
discontinuously are configured: when the measured value of the
primary carrier is lower than the first threshold value, performing
a cell search for a first corresponding carrier, having a same
frequency as the primary carrier, of a first neighboring cell, and
for a second corresponding carrier, having a same frequency as the
secondary carrier, of a second neighboring cell; and when the
measured value of the primary carrier is equal to or higher than
the first threshold value, not performing the cell search; and when
the periods are not configured, determining whether to perform the
cell search based on the measured value of the primary carrier and
the measured value of the secondary carrier.
8. The method according to claim 7, wherein the communication
terminal is connected to a serving primary cell through the primary
carrier and is connected to a serving secondary cell through the
secondary carrier, wherein the serving primary and secondary cells
are supported by the first base station.
9. The method according to claim 8, wherein the first neighboring
cell is different from the serving primary cell and the second
neighboring cell is different from the serving secondary cell,
wherein the first and second neighboring cells are target cells for
the communication terminal to connect to through the first and
second corresponding carriers and are supported by a second base
station different from the first base station, and the method
comprises measuring the reception quality of radio signals
transmitted through the first and second corresponding carriers of
the first and second neighboring cells.
10. The method according to claim 7, wherein the primary carrier is
a backward compatible component carrier and the secondary carrier
is a non-backward compatible component carrier.
11. The method according to claim 7, comprising: receiving from the
first base station information that sets the primary carrier.
12. The method according to claim 7, comprising: setting the
primary carrier according to a defined rule.
Description
RELATED APPLICATIONS
[0001] This application claims the benefits of Japanese Patent
Application No. 2009-147778 filed on Jun. 22, 2009 in Japan, the
contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a communication terminal
and a base station for controlling a communication terminal that
support component carrier aggregation (also called just "carrier
aggregation," "band aggregation," or "band bonding").
BACKGROUND ART
[0003] In a mobile communication system, a communication terminal
searches for a neighboring cell and measures the reception quality
of a radio wave from the detected neighboring cell (hereinafter
referred to as "quality measurement") when there is a decline in
the quality of communication with a cell it is currently connected
to (hereinafter referred to as a "serving cell"). If a neighboring
cell of better reception quality than the serving cell is found as
a result, a network controller causes the communication terminal to
perform a handover to the neighboring cell.
[0004] The search and quality measurement for a neighboring cell
are major factors in terms of reducing the power consumption of a
communication terminal. Basically, if a serving cell is of a
sufficiently good quality, the communication terminal is presumed
to have no need for performing the search and quality measurement
for a neighboring cell, since a communication terminal only needs
to be connected to a serving cell. A threshold value for
determining whether or not to perform a neighboring cell search
(this threshold value is called "S-measure" in LTE) is therefore
specified (Non-patent document 3). This threshold value is herein
called a "search threshold value."
[0005] FIG. 24 illustrates a search threshold value. As shown in
FIG. 24, when the measured value of the reception quality of a
serving cell is above a search threshold value, a neighboring cell
search is not performed since the quality is good and a handover is
presumed to be unnecessary. On the other hand, when the measured
value of the reception quality of a serving cell is below a search
threshold value, a neighboring cell search is performed since the
quality is bad and a handover may be made. Consequently, a
neighboring cell search is performed only when required, and the
power consumption of a communication terminal can be reduced.
[0006] By the way, LTE-advanced is now being standardized by 3GPP
so as to be a candidate for a wireless communication system adopted
into IMT-advanced. In this LTE-advanced standardization, carrier
aggregation, in which a plurality of component carriers are
simultaneously assigned to a communication terminal, is under
review for improvement in the throughput of a communication
terminal.
[0007] FIG. 25 is a conceptual diagram illustrating carrier
aggregation. In the example shown in FIG. 25, there are component
carriers f1 to f3 of a bandwidth of 20 MHz. A communication
terminal supporting carrier aggregation (e.g. a Rel-10
communication terminal) uses the component carriers f1 to f3
simultaneously to communicate with a bandwidth of 60 MHz.
[0008] On the other hand, a communication terminal which dose not
support carrier aggregation (e.g. a Rel-8/9 communication terminal)
connects to one of the component carriers f1 to f3 to communicate
over 20 MHz.
[0009] Keeping the bandwidth unchanged as above allows previously
released communication terminals (e.g. Rel-8/9) to be supported as
well, and can improve the throughput of communication terminals to
be newly released (e.g. Rel-10 communication terminals). This is
one merit of carrier aggregation.
[0010] Note here that a communication terminal incompatible with
carrier aggregation regards each circle of the carriers f1 to f3
shown in FIG. 25 as a cell. The cell is defined by 3GPP (Non-patent
document 1). Further efficiency is now under study in consideration
of implementing carrier aggregation. Scenarios for enhancing
efficiency will be described below.
[0011] (Scenario 1)
[0012] FIG. 26 shows one scenario for further enhancing the
efficiency of carrier aggregation. A component carrier f1 includes
a synchronization channel, broadcast information, an L1 control
channel, and the like, and can alone provide services to a
communication terminal. Component carriers f2 and f3 do not include
a synchronization channel nor broadcast information, and a
communication terminal cannot detect those component carriers
alone. This is because a communication terminal detects a component
carrier (which is called "cell detection" in Rel-8) by receiving a
synchronization channel in a cell search process.
[0013] A communication terminal cannot be on standby (which is
called "camp on") nor establish a call on the component carriers f2
and f3. The standby and call establishment are allowed by receiving
broadcast information (more specifically, Master Information Block
(MIB), System Information Block 1 (SIB1), and System Information
Block 2 (SIB2) in broadcast information) after cell detection. A
communication terminal therefore cannot be on standby on the
component carrier concerned unless there are both a synchronization
channel and broadcast information.
[0014] In this scenario, a communication terminal in an idle state
(RRC_IDLE) detects only the component carrier f1 and then begins to
be on standby. After that, the communication terminal performs a
call establishment process, comes into an active state
(RRC_CONNECTED), and then adds the component carriers f2 and f3 in
accordance with an instruction from the network side, to perform
carrier aggregation. Since the communication terminal may require
reception of broadcast information even after it comes into an
active state, there may be an operation in which the communication
terminal continues to use the component carrier f1 and uses the
component carriers f2 and f3 just as additions. FIG. 27 shows one
example of a process of adding the component carriers f2 and
f3.
[0015] A communication terminal which does not support carrier
aggregation (e.g. a Rel-8/9 communication terminal) will use only
the component carrier f1 even after it comes into an active
state.
[0016] (Scenario 2)
[0017] FIG. 28 shows another scenario for further enhancing the
efficiency of carrier aggregation. A component carrier f1 includes
a synchronization channel, broadcast information, an L1 control
channel, and the like, and can alone provide services to a
communication terminal. Component carriers f2 and f3 do not include
an L1 control channel, and a communication terminal cannot detect
those component carriers alone. This is because a communication
terminal cannot determine which resource it should use when there
is no L1 control channel, since it is notified of which resource it
should use through an L1 control channel.
[0018] As with the previously described scenario, a communication
terminal in an idle state cannot be on standby on the component
carriers f2 and f3, and a communication terminal which does not
support carrier aggregation (a Rel-8/9 communication terminal) also
cannot use the component carriers f2 and f3.
[0019] In the above examples, the component carrier which can
provide all services and to which a communication terminal must be
connected at the very least (the component carrier f1 in FIGS. 26
and 28) is sometimes called a backward compatible component
carrier. This is because it can sometimes support a communication
terminal of Rel-8/9 and the like as well (Non-patent document 2).
Conversely, component carriers other than the above are sometimes
called non-backward compatible component carriers.
[0020] While the downlink and uplink are not particularly
distinguished from each other in the above description, the
description basically centers on downlink operation. The downlink
and uplink correspond one-to-one with each other in LTE Rel-8.
[0021] FIG. 29 shows an "operation in LTE Rel-8." That is, when a
frequency 1 used for the downlink and a frequency 4 used for the
uplink are paired with each other and a communication terminal uses
the frequency 1 to receive, it uses the frequency 4 to transmit.
Similarly, frequencies 2 and 5, as well as frequencies 3 and 6, are
paired with each other. The process in FIG. 27 is thus shown only
for the downlink for the purpose of simplification though different
component carriers are actually used for reception and for
transmission.
[0022] FIG. 30 shows an example of possible carrier aggregation in
which the downlink and uplink are asymmetric. There may also be
such an asymmetric operation in future extensions. However, the
invention can be applied to either case where the uplink and
downlink are symmetric or asymmetric. The description below will
center on downlink component carriers.
PRIOR ART DOCUMENTS
Non-Patent Documents
[0023] Non-patent document 1: 3GPP TR 21.905 V8.8.0 [0024]
Non-patent document 2: R2-092866, "Synchronization channel and
system information for carrier aggregation" [0025] Non-patent
document 3: 3GPP TS 36.331 V8.5.0 [0026] Non-patent document 4:
3GPP TS 36.321 V8.5.0 [0027] Non-patent document 5: 3GPP TS 36.101
V8.5.1
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0028] As described above, whether to perform a cell search and
quality measurement or not is determined by using a search
threshold value and, when carrier aggregation is performed, all
component carriers comprising the carrier aggregation are regarded
as serving cells. A plurality of serving cells thus exist, and
therefore it is required to determine how to make a comparison to a
search threshold value.
[0029] A purpose of the invention is to provide a communication
terminal and a base station which are capable of determining a
search threshold value for carrier aggregation to determine the
timing of starting a cell search.
Means for Solving the Problems
[0030] A communication terminal of the invention is capable of
simultaneously communicating through a plurality of carriers by
carrier aggregation, and comprises: a quality measurement unit for
measuring the reception quality of a radio wave transmitted through
a plurality of carriers from a base station of a connected cell to
obtain a measured value; a primary carrier storage unit storing
information specifying a primary carrier chosen from the plurality
of carriers; a comparator for comparing a measured value of the
primary carrier measured by the quality measurement unit to a
threshold value; and a cell search unit for searching for another
cell when the measured value of the primary carrier is less than or
equal to the threshold value.
Advantages of the Invention
[0031] The invention involves determining the timing of performing
a cell search based on the reception quality of a primary carrier,
and thereby allows even a communication terminal supporting carrier
aggregation to appropriately start a cell search.
[0032] There are other aspects of the invention as described below.
This disclosure of the invention therefore intends to provide part
of the aspects of the invention and does not intend to limit the
scope of the invention described and claimed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 shows the timing for a communication terminal
according to a first embodiment to perform a cell search;
[0034] FIG. 2 shows a configuration of the communication terminal
of the first embodiment;
[0035] FIG. 3 shows an operation of the communication terminal of
the first embodiment;
[0036] FIG. 4 shows a scenario example of carrier aggregation;
[0037] FIG. 5 shows another scenario example of carrier
aggregation;
[0038] FIG. 6 shows a process of specifying a primary component
carrier;
[0039] FIG. 7 shows another operation of a communication terminal
to determine a primary component carrier;
[0040] FIG. 8 shows a configuration of a base station;
[0041] FIG. 9 illustrates frequency bands;
[0042] FIG. 10 shows the timing for a communication terminal
according to a second embodiment to perform a cell search;
[0043] FIG. 11 shows a configuration of the communication terminal
of the second embodiment;
[0044] FIG. 12 shows a process of specifying a primary component
carrier;
[0045] FIG. 13 shows an operation of the communication terminal of
the second embodiment;
[0046] FIG. 14 shows an example of carrier-aggregated frequency
bands and frequency bands to be measured;
[0047] FIG. 15 shows the timing for a communication terminal
according to a third embodiment to perform a cell search;
[0048] FIG. 16 shows a configuration of the communication terminal
of the third embodiment;
[0049] FIG. 17 shows the timing of gaps set by the communication
terminal of the third embodiment;
[0050] FIG. 18 shows the timing of gaps set by the communication
terminal of the third embodiment;
[0051] FIG. 19 shows an operation of the communication terminal of
the third embodiment;
[0052] FIG. 20 shows the timing for a communication terminal
according to a fourth embodiment to perform a cell search;
[0053] FIG. 21 shows the timing for the communication terminal
according to the fourth embodiment to perform a cell search;
[0054] FIG. 22 shows a configuration of the communication terminal
of the fourth embodiment;
[0055] FIG. 23 shows an operation of the communication terminal of
the fourth embodiment;
[0056] FIG. 24 illustrates a search threshold value;
[0057] FIG. 25 is a conceptual diagram illustrating carrier
aggregation;
[0058] FIG. 26 shows one scenario for further enhancing the
efficiency of carrier aggregation;
[0059] FIG. 27 shows a process of adding component carriers;
[0060] FIG. 28 shows another scenario for further enhancing the
efficiency of carrier aggregation;
[0061] FIG. 29 shows an operation in LTE Rel-8;
[0062] FIG. 30 shows an example of possible carrier aggregation in
which the downlink and uplink are asymmetric;
[0063] FIG. 31 shows a scenario example of carrier aggregation;
[0064] FIG. 32 shows the timing for a communication terminal
according to a fifth embodiment to perform a cell search;
[0065] FIG. 33 shows a configuration of the communication terminal
according to the fifth embodiment; and
[0066] FIG. 34 shows an operation of the communication terminal
according to the fifth embodiment.
MODE OF EMBODYING THE INVENTION
[0067] The following is a detailed description of the invention.
The embodiments described below are only examples of the invention,
and the invention can be varied in various aspects. Therefore, the
specific configurations and functions disclosed below do not limit
the claims.
[0068] Now, a communication terminal and base station of
embodiments of the invention will be described with reference to
the drawings.
First Embodiment
[0069] FIG. 1 shows the timing for a communication terminal 1
according to a first embodiment to perform a cell search. A primary
component carrier is already determined among component carriers
performing carrier aggregation. A component carrier f2 is the
primary component carrier in the example shown in FIG. 1. The
primary component carrier may be specified by a base station 30 or
may be determined by the communication terminal 1 based on some
kind of rule. The method of determination will be described
later.
[0070] The communication terminal 1 compares a measured value of
the reception quality of the primary component carrier to a search
threshold value and, if the measured value of the primary component
carrier is more than or equal to the search threshold value,
determines a cell search to be unnecessary even if any measured
value of other component carriers are below the search threshold
value. Conversely, if the measured value of the primary component
carrier is below the search threshold value, the communication
terminal 1 determines a cell search to be required.
[0071] [Communication Terminal]
[0072] FIG. 2 shows a configuration of the communication terminal 1
of the first embodiment. The communication terminal 1 has a
receiver 11, a measurement configuration unit 12, a primary carrier
determination unit 13, a primary carrier storage unit 14, a quality
measurement unit 15, a comparator 16, a cell search unit 17, a
measurement result judging unit 18, and a transmitter 19.
[0073] The receiver 11 receives a signal transmitted from the base
station 30. From among the received information, the receiver 11
sends information on measurement (a measurement configuration) to
the measurement configuration unit 12 and sends information for
determining a primary frequency to the primary carrier
determination unit 13. The receiver 11 also sends a signal for
measurement transmitted from the base station 30 separately to the
quality measurement unit 15 and cell search unit 17.
[0074] The measurement configuration unit 12 processes the
information on measurement sent from the receiver 11 and configures
therewith the quality measurement unit 15, the comparator 16, the
cell search unit 17, and the measurement result judging unit 18.
Specific examples of the information to be processed here include
measConfig of IE (Information Elements) in an RRC Connection
Reconfiguration message provided in Non-patent document 3.
MeasConfig includes a frequency/cell to be measured (which is
called and hereinafter referred to as a "measurement object"),
information on how to report a measurement result to the base
station 30 (which is called and hereinafter referred to as a
"reporting configuration"), information on how to measure (which is
called a "quantity configuration" and is hereinafter referred to as
a "measurement configuration"), a search threshold value, and the
like.
[0075] The measurement configuration unit 12 also notifies the
quality measurement unit 15 and cell search unit 17 of a
measurement object, a measurement configuration, and the like,
notifies the measurement result judging unit 18 of a reporting
configuration and the like, and notifies the comparator 16 of the
search threshold value mentioned above.
[0076] The primary carrier determination unit 13 determines which
one of a plurality of carrier-aggregated component carriers is to
be used as a primary component carrier for a comparison to the
search threshold value. The method of determining a primary
component carrier will be described later in detail. The primary
carrier determination unit 13 stores the result of primary
component carrier determination in the primary carrier storage unit
14.
[0077] The quality measurement unit 15 performs measurement on a
currently connected component carrier as configured by the
measurement configuration unit 12. The quality measurement unit 15
sends the measurement result to the comparator 16 and the
measurement result judging unit 18.
[0078] The comparator 16 reads the information on a primary carrier
from the primary carrier storage unit 14 to specify a primary
component carrier. The comparator 16 then compares the quality
measurement result for the primary component carrier to the search
threshold value passed from the measurement configuration unit 12
and determines whether or not to start a cell search. The
comparator 16 notifies the cell search unit 17 of the judgment
result.
[0079] When a cell search is determined to be performed by the
comparison result received from the comparator 16, the cell search
unit 17 performs a cell search according to the details configured
by the measurement configuration unit 12 and performs quality
measurement for a detected cell. The cell search unit 17 sends the
measurement result to the measurement result judging unit 18.
[0080] The measurement result judging unit 18 compares the
measurement results received from the quality measurement unit 15
and cell search unit 17 and, based on the measurement configuration
configured by the measurement configuration unit 12, determines
whether a report to the base station 30 is to be made or not. If
the reporting is determined to be made, the measurement result
judging unit 18 creates a Measurement Report message and sends it
to the transmitter 19. The transmitter 19 transmits the Measurement
Report message passed from the measurement result judging unit 18
to the base station 30.
[0081] FIG. 3 shows a flowchart showing an operation of the
communication terminal 1 of the embodiment. The measurement
configuration unit 12 of the communication terminal 1 receives a
measurement configuration transmitted from the base station 30, and
passes configuration values in the received measurement
configuration information on to the quality measurement unit 15,
comparator 16, cell search unit 17, and measurement result judging
unit 18 to configure them with the configuration values (S10).
[0082] The primary carrier determination unit 13 of the
communication terminal 1 then determines a primary component
carrier to be compared to a search threshold value (S12). The
primary carrier determination unit 13 receives information on the
primary component carrier from the base station 30, and determines
the received component carrier to be a primary. The primary carrier
determination unit 13 stores information on the determined primary
carrier in the primary carrier storage unit 14.
[0083] The comparator 16 of the communication terminal 1 then
judges whether a measured value of the reception quality of the
primary component carrier is more than or equal to the search
threshold value or not (S14). The comparator 16 receives
information on the measured value of the reception quality of the
primary component carrier from the quality measurement unit 15. If
the measured value of the primary component carrier is more than or
equal to the search threshold value (Yes at S14), the communication
terminal 1 does not perform a cell search but monitors the measured
value of the primary component carrier until it falls below the
search threshold value.
[0084] If the measured value of the primary component carrier is
below the search threshold value (No at S14), the communication
terminal 1 starts a cell search (S16). If the communication
terminal 1 detects a neighboring cell, it performs quality
measurement for the detected cell.
[0085] How to determine a primary component carrier will be
described below. As described above with the help of FIGS. 26 and
28, there are a backward compatible component carrier, which can
alone provide services, and other component carriers in a carrier
aggregation operation. The communication terminal 1 needs to
receive broadcast information and an L1 control channel, and
therefore a good reception quality requires to be always kept on a
backward compatible carrier. For that reason, a backward compatible
carrier may be set as a primary component carrier.
[0086] FIG. 4 shows a scenario example of carrier aggregation. In
such a case where there is only one backward compatible component
carrier (f3 in this example) when the communication terminal 1
performs carrier aggregation, the component carrier is handled as a
primary component carrier and is used for a comparison to the
search threshold value.
[0087] FIG. 5 shows another scenario example of carrier
aggregation. In this example, a plurality of backward compatible
component carriers f1 and f3 are assigned to the communication
terminal 1. One of the two backward compatible component carriers
is used as a primary component carrier in this case.
[0088] FIG. 6 shows a process of specifying a primary component
carrier. At the beginning, the communication terminal 1 camps on a
component carrier f1 and is on standby (S20). When a trigger for
changing from an idle state to an active state is activated by the
communication terminal 1 receiving paging or making a phone call
(S22), the communication terminal 1 uses the component carrier f1
to transmit Random Access Preamble to the base station 30 (S24).
Receiving this, the base station 30 transmits Random Access
Response to the communication terminal 1 (S26).
[0089] The communication terminal 1 then transmits an RRC
Connection Request message to the base station 30 (S28), which upon
receiving this transmits an RRC Connection Setup message to the
communication terminal 1 (S30). This causes the communication
terminal 1 to change from an idle state to an active state (S32)
and connect to the component carrier f1 (S34).
[0090] Subsequently, the communication terminal 1 transmits an RRC
Connection Complete message to the base station 30 (S36), which
transfers the RRC Connection Complete message to its core network
(S38). Receiving this, the core network device 40 transmits to the
base station 30 capability information including information on
whether the communication terminal 1 can perform carrier
aggregation or not (S40). Receiving the capability information for
the communication terminal 1, the base station 30 determines to
operate carrier aggregation (S42).
[0091] If the base station 30 determines to perform carrier
aggregation, it transmits to the communication terminal 1 a
Security Mode Command (S44) and, subsequently, an RRC Connection
Reconfiguration message (S46). The RRC Connection Reconfiguration
message transmitted here includes an instruction to add component
carriers f2 and f3 and an instruction to specify a primary
component carrier.
[0092] Receiving the RRC Connection Reconfiguration message, the
communication terminal 1 adds the component carriers f2 and f3 (S48
and S50), and transmits Security Mode Complete to the base station
30 (S52). Subsequently, the communication terminal 1 transmits an
RRC Connection Reconfiguration Complete message (S54).
[0093] While an example where a primary component carrier is
explicitly specified is shown in FIG. 6, a primary component
carrier may also be determined from other information. For example,
the communication terminal 1 is at the beginning connected to the
component carrier f1 in the example shown in FIG. 6 and, in such a
case, the component carrier f1 may be handled as a primary unless
otherwise specified.
[0094] FIG. 7 shows a flowchart of the above-described operation of
the communication terminal 1 determining a primary component
carrier. First, the communication terminal 1 judges whether there
is carrier aggregation or not (S60). If there is no carrier
aggregation (No at S60), there is only one component carrier, and
therefore the communication terminal 1 sets the carrier that it
uses for connection as a primary (S62).
[0095] If there is carrier aggregation (Yes at S60), the
communication terminal 1 judges whether there is explicit
assignment of a primary component carrier or not (S64). If there is
explicit assignment (Yes at S64), the communication terminal 1 sets
the explicitly assigned component carrier as a primary (S66).
[0096] If there is no explicit assignment (No at S64), the
communication terminal 1 judges whether the carrier-aggregated
carriers include more than one backward compatible carriers or not
(S68). If there is only one backward compatible carrier (No at
S68), the communication terminal 1 sets the backward compatible
carrier as a primary carrier (S70). If there is a plurality of
backward compatible carriers (Yes at S68), the communication
terminal 1 sets the component carrier that it has been connected to
from the beginning as a primary (S72).
[0097] [Base Station]
[0098] FIG. 8 shows a configuration of the base station 30 of the
embodiment. The base station 30 of the embodiment has a function to
specify a primary component carrier for the communication terminal
1. The base station 30 has a terminal information manager 31, an
aggregation determination unit 32, a primary determination unit 33,
a configuration determination unit 34, and a transmitter 35.
[0099] The terminal information manager 31 manages a channel
configuration, capability, and the like of the communication
terminal 1. The terminal information manager 31 sends these pieces
of information to the aggregation determination unit 32.
[0100] The aggregation determination unit 32 determines whether the
communication terminal 1 performs carrier aggregation or not,
determines on which component carriers the aggregation is to be
performed if carrier aggregation is to be performed, and sends the
result to the primary determination unit 33.
[0101] The primary determination unit 33 determines a primary
component carrier, and sends information on the determined primary
component carrier and the information received from the aggregation
determination unit 32 both to the configuration determination unit
34.
[0102] The configuration determination unit 34 creates a message
for instructing the communication terminal 1 which component
carrier is to be a primary, and sends the message to the
transmitter 35. Note here that the instruction on a primary
component carrier will be omitted if, in the setting process of the
primary component carrier of the communication terminal 1 shown in
FIG. 7, the communication terminal 1 selects a component carrier
that is desired by the base station 30 to be a primary without any
instruction from the base station 30. The transmitter 35 transmits
the message created by the configuration determination unit 34 to
the communication terminal 1. This is a description of
configurations and operations of the communication terminal 1 and
base station 30 of the first embodiment.
[0103] Since the communication terminal 1 of the embodiment
determines the timing of performing a cell search based on the
reception quality of a primary carrier, it can appropriately start
a cell search even when carrier aggregation is performed with a
plurality of component carriers.
[0104] Since the base station 30 of the embodiment transmits
information indicating a primary component carrier to the
communication terminal 1, the communication terminal 1 can use an
appropriate component carrier to make a judgment on a cell
search.
[0105] While the above description is of how to determine a primary
component carrier, a primary component carrier may be determined by
methods other than the above.
[0106] For example, a measurement object in a measurement
configuration is to be used to set a frequency/cell to be measured.
If only one component carrier is specified here as a frequency to
be measured, the frequency can be determined to be a primary
component carrier. Conversely, there may also be a configuration in
which a component carrier that was a primary is excluded from being
a measurement object. In such a case, the component carrier
concerned may cease to be a primary and another backward compatible
component carrier may be set as a primary. In this case, if there
are a plurality of other backward compatible component carriers, a
primary component carrier is determined in accordance with an
instruction from the base station 30.
[0107] Instead of receiving an instruction from the base station
30, the communication terminal 1 may control dynamically in such a
manner that it makes the highest-performing component carrier a
primary or it makes the lowest-performing component carrier a
primary. The judgment of good or bad performance here may be made
by using a measurement result used for a Measurement Report message
or by using as another choice an instantaneous measurement result
used for CQI reporting.
[0108] The component carrier most used for reception among
carrier-aggregated component carriers may be set as a primary.
[0109] The handling as a primary component carrier may be applied
not only to the comparison to the search threshold value but also
to the reporting of a Measurement Report message. Since a
Measurement Report message will constantly report the quality of a
serving cell, a primary component carrier determined in the
embodiment may be used as the component carrier to be reported
then.
[0110] Discontinuous Reception (DRX), which is performed by the
communication terminal 1, may also be considered. During carrier
aggregation, DRX is not similarly performed on all component
carriers but may be operated for each component carrier.
Specifically, for example, DRX is performed only on a component
carrier that is not used a lot, and is not performed on a
frequently-used component carrier. In such a case where the DRX
operation differs from one component carrier to another, there may
be an operation in which a component carrier that DRX is performed
on is not set as a primary component carrier. Conversely, a
component carrier set as a primary may start DRX on condition that
all the other component carriers start DRX. As a result, even when
a component carrier set as a primary has not been used for a while,
the component carrier set as a primary will not start DRX as long
as another component carrier has been used. A component carrier set
as a primary is presumed to have a good or stable quality for its
communication terminal or as a system, and it is desirable that a
component carrier set as a primary be used as much as possible and
that DRX be performed thereon less frequently than on the other
component carriers. The above-described operation allows a
component carrier set as a primary to be kept in a state where it
can be used at all times even if communication cannot be
established with a certain communication terminal by using the
component carrier set as a primary when the component carrier set
as a primary is under high load.
Second Embodiment
[0111] A communication terminal 2 of a second embodiment will be
described below. The communication terminal 2 of the second
embodiment is different from that of the first embodiment in that
it controls the operation for each frequency band.
[0112] FIG. 9 illustrates frequency bands. FIG. 9 shows carriers f1
to f5 as candidates for component carriers. A plurality of carriers
of the carriers f1 to f5 are used to perform carrier aggregation.
Note here that the carriers f1 and f2 are included in a first
frequency band (e.g. 800 MHz band) and the carriers f3 to f5 are
included in a second frequency band (e.g. 2 GHz band). In an
operation like this, it is desirable to control the operation for
each frequency band since there may be a backward compatible
carrier in each frequency band and measurement results may differ
considerably from one frequency band to another. In the embodiment,
a primary component carrier is selected for each frequency
band.
[0113] FIG. 10 shows the timing for the communication terminal 2
according to the second embodiment to perform a cell search. This
is an example where carrier aggregation is performed by using, as
component carriers, the carriers f1 to f3 of the carriers f1 to f5
shown in FIG. 9. The component carrier f1 of the component carriers
f1 and f2 included in the first frequency band is a primary. Since
the second frequency band includes only the component carrier f3,
this is a primary.
[0114] As shown in FIG. 10, a cell search is not performed if the
quality is above the search threshold value for all the primary
component carriers (the component carriers f1 and f3 in this
example). A cell search is started for the second frequency band
when the quality of the primary of the second frequency band, the
component carrier f3, falls below the search threshold value.
Specifically, the search process is performed only for f3 if only
f3 is in the measurement configuration for the second frequency
band or, if there is any carrier other than f3 (e.g. f4 shown in
FIG. 9) in the configuration and if the communication terminal 2
can perform the measurement for the other frequency (i.e. f4) while
keeping the connection to the component carrier it is connected to,
the search process is performed for f4 as well as for f3. Since the
quality of the component carrier f1 is above the search threshold
value at this point in time, a cell search is not performed on the
component carriers included in the first frequency band.
[0115] The process is the same (that is, a cell search is not
performed) even if the quality of the component carrier f2, which
is not the primary of the first frequency band, falls below the
search threshold value. A cell search is performed on all the
component carriers in the configuration for the communication
terminal 2 including the first frequency band only when the quality
of the primary of the first frequency band, the component carrier
f1, falls below the search threshold value.
[0116] FIG. 11 shows a configuration of the communication terminal
2 of the second embodiment. The configuration of the communication
terminal 2 of the second embodiment is basically the same as that
of the first embodiment, but is different therefrom in that it has
a plurality of comparators 16. A description will be given below of
the configuration of the communication terminal 2 of the second
embodiment, centering on differences with the first embodiment.
[0117] The primary carrier determination unit 13 determines a
primary component carrier for each frequency band. The primary
carrier determination unit 13 notifies the comparator 16 for each
frequency band of information on the determined primary component
carrier.
[0118] The quality measurement unit 15 notifies the plurality of
comparators 16 of quality measurement results. The cell search unit
17 does not start a cell search for all at once, but controls the
start of a cell search for each frequency band in accordance with
instructions from the plurality of comparators 16.
[0119] Each of the plurality of comparators 16 compares the primary
component carrier of the corresponding frequency band to the search
threshold value. Upon receiving the reception quality of the
primary component carrier of the corresponding frequency band from
the quality measurement unit 15, each of the plurality of
comparators 16 compares the reception quality to the search
threshold value and notifies the cell search unit 17 of the
comparison result.
[0120] FIG. 12 shows a process of specifying a primary component
carrier in the second embodiment. The details of the process are
basically the same as those in the first embodiment shown in FIG.
6, but are different therefrom in that a primary component carrier
is specified in RRC Connection Reconfiguration message (S46a) for
each frequency band.
[0121] FIG. 13 is a flowchart showing an operation of the
communication terminal 2. The communication terminal 2 receives
information on a measurement (a measurement configuration)
transmitted from the base station 30, and determines the
measurement configuration by means of the measurement configuration
unit 12 (S80). The communication terminal 2 then judges whether a
plurality of frequency bands are used in carrier aggregation or not
(S82). If a plurality of frequency bands are judged not to be used
(No at S82), the communication terminal 2 determines a primary
component carrier (S84). The method described in the first
embodiment can be used for this.
[0122] If a plurality of frequency bands are judged to be used (Yes
at S82), the communication terminal 2 determines a primary
component carrier for each frequency band (S86).
[0123] The comparators 16 of the communication terminal 2 then
judge whether the quality of the primary component carriers is more
than or equal to the search threshold value or not (S88). If the
quality of the primary component carriers is more than or equal to
the search threshold value (Yes at S88), the communication terminal
2 does not perform a cell search but monitors the quality of the
primary component carriers until it falls below the search
threshold value. If the quality of any primary component carrier is
not more than or equal to the search threshold value (No at S88),
the communication terminal 2 starts a cell search for the frequency
band including the component carrier that is below the search
threshold value (S90).
[0124] The base station 30 of the second embodiment will be
described below. The configuration of the base station 30 of the
second embodiment is basically the same as that of the first
embodiment (see FIG. 8). However, the base station 30 of the second
embodiment determines a primary component carrier for each
frequency band by means of the primary determination unit 33 and
transmits them from the transmitter 35.
[0125] Groups divided according to frequency bands in the
embodiment will be described in detail here. These groups include a
bundle of neighboring component carriers. Specifically, component
carriers can be grouped depending on frequency bands according to
(1) to (3) given below. The methods shown below do not contradict
each other, and can be combined in any way.
[0126] (1) As shown in Chapter 5.7.3 of Non-patent document 5,
corresponding frequencies are defined in LTE. In this case,
frequencies bundled together as E-UTRA Operating Band may be
regarded as a group of the same frequency band.
[0127] (2) The base station 30 may determine groups of the same
frequency bands in accordance with the system operation. In this
case, the base station 30 notifies the communication terminal 2 of
the range of frequency bands of the same groups. This notification
may be transmitted through broadcast information or through
messages specific to communication terminals.
[0128] (3) A rule may be made according to which only a certain
frequency band is regarded as the same group. Specifically, for
example, with a 100 MHz band being defined in advance (e.g. 95-105
MHz), those included in this band are regarded as being in the same
frequency band and those not included in this band are regarded as
being in another frequency band.
[0129] When carrier aggregation is performed by using different
frequency bands, the communication terminal 2 of the embodiment can
control a cell search in consideration of differences in reception
quality caused by the difference of frequency band. This can reduce
power consumption of communication terminals.
[0130] The embodiment has been shown with an example in which a
common value is set as the search threshold value regardless of
frequency band. However, search threshold values different from one
group to another depending on frequency band may be set.
[0131] The start of a cell search is in the embodiment controlled
for each frequency band. However, a cell search may be performed on
all component carriers if any of the primary component carriers
falls below the search threshold value. Conversely, there may be an
operation in which a cell search is not started until all the
primary component carriers fall below the search threshold
value.
Third Embodiment
[0132] A communication terminal 3 of a third embodiment will be
described below. The communication terminal 3 of the third
embodiment, unlike the second embodiment, performs a cell search
not only on carrier-aggregated component carriers but also on
non-carrier-aggregated carriers when a primary component carrier
falls below the search threshold value. The configuration of the
base station 30 of the third embodiment is the same as that of the
second embodiment.
[0133] FIG. 14 shows an example of carrier-aggregated frequency
bands and frequency bands to be measured. As shown in FIG. 14, a
carrier aggregation is configured with component carriers f1, f2,
and f5, and a measurement object is configured with the component
carriers f1, f2, and f5, in addition to a component carrier f3.
[0134] In this case, since the component carriers f1, f2, and f5
are currently connected component carriers, the communication
terminal 3 can perform a cell search and a quality measurement on
the same component carriers f1, f2, and f5 for a neighboring cell
at the same time on the component carriers f1, f2, and f5 for the
connected cell. However, the component carrier f3 is not currently
included in the carrier aggregation. For example, in a case where
the communication terminal 3 can be connect to only three component
carriers at the same time, that is, where the number of component
carriers with which the communication terminal 3 can perform
carrier aggregation, the capability, is three, a cell search and
quality measurement cannot be performed on the component carrier f3
unless the communication with any one of the component carriers f1,
f2, and f5 is interrupted.
[0135] Generally, this interruption process cannot be performed
unless gap configuration is performed in which the base station 30
explicitly provides the timing of gaps for the communication
terminal 3. The embodiment allows a cell search to be performed on
a component carrier that is not in a band aggregation like the
component carrier f3, without an instruction from the base station
30.
[0136] FIG. 15 shows the timing for the communication terminal 3
according to the third embodiment to perform a cell search. As with
the first and second embodiments described above, a cell search is
not performed when the quality of all component carriers is above
the search threshold value.
[0137] Then when the quality of the component carrier f5 in the
third frequency band falls below the search threshold value, the
communication terminal 3 starts a cell search on the component
carrier f5 as in the second embodiment.
[0138] At the same time, the communication terminal 3 of the
embodiment checks the data reception mode of the component carrier
f5. Specifically, the communication terminal 3 checks whether the
component carrier f5 is configured for DRX (Discontinuous
reception) or not and whether there has been no data reception for
a while or not. In such reception mode, it may not be indispensable
to continuously maintain the connection on the component carrier
f5. Along with the cell search process on the component carrier f5,
the communication terminal 3 automatically sets gap periods for the
component carrier f5, and performs a cell search on the
non-carrier-aggregated component carrier f3.
[0139] This allows a cell search to be performed on another
component carrier without an instruction to set gaps from the base
station 30 even under circumstances where it is not used for
carrier aggregation and a cell search cannot be performed on extra
component carriers because of the limit of the ability of the
communication terminal 3 (the number of component carriers on which
the communication terminal 3 can be connected at the same
time).
[0140] FIG. 16 shows a configuration of the communication terminal
3 of the third embodiment. The configuration of the communication
terminal 3 of the third embodiment is basically the same as that of
the second embodiment, but is different therefrom in that the
communication terminal 3 of the third embodiment has a reception
mode detector 20. A description will be given below of the
configuration of the communication terminal 3, centering on
differences with the second embodiment.
[0141] At the start of a cell search, the comparators 16 instruct
the reception mode detector 20 about a component carrier on which
the cell search is determined to be performed, and instruct the
reception mode detector 20 to check the reception mode of the
component carrier concerned.
[0142] Based on the instructions from the comparators 16, the
reception mode detector 20 checks the reception mode of the
specified component carrier. The reception mode is checked here
about the presence or absence of previously described DRX, about
the presence or absence of data reception, and so on. If the
judgment result indicates that DRX is performed or that data has
not been received for a certain period of time, the reception mode
detector 20 determines that the communication terminal 3 can set
gap periods for the component carrier concerned, and notifies the
cell search unit 17 of the information.
[0143] Based on the notification from the reception mode detector
20, the cell search unit 17 automatically sets gap periods for the
currently carrier-aggregated component carrier, and performs a cell
search on a non-carrier-aggregated component carrier.
[0144] FIG. 17 shows the timing of gaps set by the communication
terminal 3 of the embodiment. Time t1 is a time when data was
received last on the component carrier f5. Time t2 is a time when a
cell search was started on the component carrier f5. This is a time
when the quality of the component carrier f5 fell below the search
threshold value in FIG. 15.
[0145] The communication terminal 3 checks at the time t2 the
status of this component carrier. If elapsed time from the time t1
(the timer T in FIG. 17) exceeds a certain period of time (the
period X in the figure), gap periods are set for the component
carrier f5 at the time point, and a cell search is performed on the
component carrier f3.
[0146] The "certain period of time" is a threshold value for
determining whether or not to create gaps. This certain period of
time X may be notified of to the communication terminal 3 through
broadcast information (a form like a notification such as an IE
"T300" transmitted in SIB2 described in Non-patent document 3), or
may be notified of individually to the communication terminal 3 (a
notification like an IE "drx-InactivityTimer" etc. included in an
RRC Connection Reconfiguration message described in Non-patent
document 3), or may be a fixed value.
[0147] In an example shown in FIG. 18, the timer T has not yet
reached the period X at the time t2. When the timer T reaches the
period X (time t3), gaps are set and a cell search is started on
the component carrier f3.
[0148] The length and timing of the gap periods may be set freely
by the communication terminal 3, or may be set by the communication
terminal 3 based on information specified by the base station 30.
If the base station 30 specifies them, it may specify the length of
one gap, the cycle of creating gaps, and the timing of creating
gaps (e.g. from which subframe in SFN (System Frame Number) mod=Y,
etc.). This setting may be notified of through broadcast
information, or may be notified of individually to the
communication terminal 3.
[0149] In FIGS. 17 and 18 an operation is shown where whether gap
periods can be set or not is judged on whether data has been
received on the component carrier or not but, as described above,
gap periods can be set if the DRX operation is performed. The DRX
operation is provided in Non-patent document 4. In this case, gap
periods are set so that a cell search is performed on the component
carrier f3 at a time when the communication terminal 3 is not
receiving data from the component carrier f5.
[0150] FIG. 19 shows an operation of the communication terminal 3
of the third embodiment. The communication terminal 3 receives
information on measurement (a measurement configuration)
transmitted from the base station 30, and determines the
measurement configuration by means of the measurement configuration
unit 12 (S100). The communication terminal 3 then judges whether a
plurality of frequency bands are used in carrier aggregation or not
(S102).
[0151] If a plurality of frequency bands are judged not to be used
(No at S102), the communication terminal 3 determines a primary
component carrier (S104). The method described in the first
embodiment can be used for this. If a plurality of frequency bands
are judged to be used (Yes at S102), the communication terminal 3
determines a primary component carrier for each frequency band
(S106).
[0152] The comparators 16 of the communication terminal 3 then
judge whether the quality of the primary component carriers is more
than or equal to the search threshold value or not (S108). If the
quality of the primary component carriers is more than or equal to
the search threshold value (Yes at S108), the communication
terminal 3 does not perform a cell search but monitors the quality
of the primary component carriers until it falls below the search
threshold value. If the quality of any primary component carrier is
not more than or equal to the search threshold value (No at S108),
the communication terminal 3 judges whether there is a carrier to
be measured other than the carrier-aggregated component carriers or
not (S110). If the result of this judgment indicates that there is
no other carrier to be measured, the communication terminal 3
starts a cell search for the frequency band including the component
carrier that is below the search threshold value (S112).
[0153] If there is a carrier to be measured other than the
carrier-aggregated component carriers, the communication terminal 3
judges whether a condition for setting gap periods for performing a
cell search on the carrier is met or not (S114). The condition for
setting gap periods is a condition in which data has not been
received for a period of time or DRX reception is performed on the
component carrier that is below the search threshold value.
[0154] If the condition for setting gap periods is not met (No at
S114), the communication terminal 3 starts a cell search for the
frequency band including the component carrier that is below the
search threshold value (S112). If the condition for setting gap
periods is met (Yes at S114), the communication terminal 3 starts a
cell search on a carrier to be measured that is not currently
included in the carrier aggregation, as well as a cell search on
the frequency band that is below the search threshold value (S116).
This is a description of a configuration and an operation of the
communication terminal 3 of the third embodiment.
[0155] Thus, if data has not been received for a period of time on
a carrier-aggregated component carrier, a cell search can be
performed, by setting gap periods for the component carrier, on
another carrier that is not in the carrier aggregation with limited
influence on the reception process in the current connection. The
case where data has not been received for a period of time includes
a case where DRX reception is performed and therefore data has not
been received during the reception intervals.
[0156] While in the above-described embodiment a cell search is
performed if a condition for setting gap periods (DRX mentioned
above etc.) is met, whether or not to measure for a component
carrier may be controlled by assigning priorities to the component
carriers, in addition to the above condition.
[0157] In the example shown in FIG. 15 for example, suppose that
the priority of the component carrier f3 is set high and the
priority of the component carrier f5 is set low. In this case,
since the priority of the component carrier f3 is higher than that
of the component carrier f5, a cell search is performed on the
component carrier f3 as described in the embodiment. Conversely, it
is possible not to perform a cell search on the component carrier
f3 if the priority of the component carrier f3 is set low and the
priority of the component carrier f5 is set high.
[0158] The priority of each component carrier here is a concept
close to the frequency priority introduced in 3GPP Rel-8. The
frequency priority introduced in 3GPP Rel-8, however, is the
priority for the communication terminal 3 in an idle state or the
like to select a frequency when it performs mobility control
without any instruction from the network and, on the other hand,
the priority in this example is different in that it is used for
determining for which frequency a cell search is preferentially
performed when the communication terminal 3 performs mobility
control with an instruction received from the network. For this
reason, this priority of each component carrier needs to be used
also for the communication terminal 3 in an active state. The
notification may be made to the communication terminal 3 by
broadcast information, or by an individual message. The
communication terminal 3 stores the priority information notified
of in a storage unit (a carrier priority storage unit) in advance
so that it can read and use the information as required.
[0159] While in the embodiment a case has been shown in which a
cell search is performed on a component carrier in the same system,
i.e. LTE, without gap periods specified by the base station, the
measurement may be made for another system such as UMTS, GSM, CDMA
2000, WiMAX, or the like.
[0160] While the embodiment has been described based on the second
embodiment in which the search operation is determined for each
frequency band, it may be applied to the first embodiment which
does not have the concept of the search operation for each
frequency band.
Fourth Embodiment
[0161] A communication terminal 4 of a fourth embodiment will be
described below. The configuration of the communication terminal 4
of the fourth embodiment is basically the same as that of the first
embodiment, but is different therefrom in that it uses a plurality
of search threshold values. The base station 30 of the fourth
embodiment is the same as that of the first embodiment (see FIG.
8).
[0162] FIGS. 20 and 21 show the timing for the communication
terminal 4 according to the fourth embodiment to perform a cell
search. A primary search threshold value is used for a primary
component carrier, and a secondary search threshold value is used
for component carriers other than a primary.
[0163] This allows a cell search to be started when a primary
component carrier falls below the primary search threshold value as
shown in FIG. 20 or when all component carriers except for the
primary fall below the secondary search threshold value as shown in
FIG. 21.
[0164] FIG. 22 shows a configuration of the communication terminal
4 of the fourth embodiment. The configuration of the communication
terminal 4 of the fourth embodiment is basically the same as that
of the first embodiment (see FIG. 2), but is different therefrom in
that it has a primary comparator 16a and a secondary comparator
16b. A description will be given below, centering on differences
with the first embodiment.
[0165] The primary carrier determination unit 13 notifies the
primary comparator 16a of a primary component carrier, and notifies
the secondary comparator 16b of the other component carriers.
[0166] The primary comparator 16a judges whether the primary
component carrier is below the primary search threshold value or
not, and notifies the cell search unit 17 of the judgment result.
The secondary comparator 16b judges whether all the component
carriers other than the primary are below the secondary search
threshold value, and notifies the cell search unit 17 of the
judgment result.
[0167] The cell search unit 17 starts a cell search if it is
notified to start a cell search by either the primary comparator
16a or the secondary comparator 16b.
[0168] FIG. 23 is a flowchart showing an operation of the
communication terminal 4. The communication terminal 4 receives
information on measurement (a measurement configuration)
transmitted from the base station 30, and determines the
measurement configuration by means of the measurement configuration
unit 12 (S120). The communication terminal 4 then determines a
primary component carrier (S122). The method described in the first
embodiment can be used for this.
[0169] The comparator 16a of the communication terminal 4 then
judges whether the quality of the primary component carrier is less
than or equal to the primary search threshold value or not (S124).
If the quality of the primary component carrier is less than or
equal to the primary search threshold value (Yes at S124), the
communication terminal 4 starts a cell search (S128).
[0170] If the quality of the primary component carrier is not less
than or equal to the primary search threshold value (No at S124),
the secondary comparator 16b of the communication terminal 4 judges
whether all the component carriers other than the primary are less
than or equal to the secondary search threshold value or not
(S126).
[0171] If the quality of the component carriers other than the
primary is less than or equal to the secondary search threshold
value (Yes at S126), the communication terminal 4 starts a cell
search (S128). If the quality of the component carriers other than
the primary is not less than or equal to the secondary search
threshold value (No at S126), the communication terminal 4 does not
perform a cell search, but returns to the process of judging the
measured value of the primary component carrier (S124). This is a
description of a configuration and an operation of the
communication terminal 4 of the fourth embodiment.
[0172] Since the communication terminal 4 of the embodiment uses
the secondary search threshold value, in addition to the primary
search threshold value, to judge the measured values of the
component carriers other than the primary, it can detect another
cell in less time when the quality of all the component carriers
other than the primary decreases.
[0173] While in the embodiment the condition is that all the
component carriers other than the primary fall below the secondary
search threshold value, it may be that one or a certain number of
the component carriers other than the primary fall below the
secondary search threshold value.
[0174] While in the invention a cell search is started if the
quality of the primary component carrier falls below the primary
search threshold value or if the quality of all the component
carriers other than the primary falls below the secondary search
threshold value, a cell search may be started if both conditions
are met.
[0175] When a DRX operation is performed in which a communication
terminal does not receive for a long while, the comparison
operation may be combined with DRX and be changed to an operation
in which the comparison is made only between the reception quality
of a primary component carrier and the primary search threshold
value. This is because it is desired to reduce the number of
performing the search process since a reduction in power
consumption is greatly required when DRX is performed. Another
reason is that a failure in handover or the like does not have much
influence since there is no transmission and reception of data
during a DRX operation in which a communication terminal does not
receive for a long while. As a method that produces an effect
similar to this, there may be an operation in which the secondary
search threshold value is lowered when DRX is performed.
Fifth Embodiment
[0176] A communication terminal 5 of a fifth embodiment will be
described below. The configuration of the communication terminal 5
of the fifth embodiment is basically the same as that of the first
embodiment, but is different therefrom in that it uses, for each
component carrier, an index that takes into account as the
reception quality not only the reception strength but also
interference.
[0177] The "S-measure," defined in the previously described
Non-patent document 3, is provided by using RSRP (Reference Signal
Received Power). This RSRP indicates the reception strength, which
means that the need for a neighboring cell search process is
determined by using the reception strength as the reception
quality.
[0178] A possible weakness of this case in which the need for a
neighboring cell search process is determined by using the
reception strength is that even if the quality of a serving cell is
sufficient, there is an interfering cell and the cell cannot be
detected. This problem is shown in FIG. 31. Suppose here that there
are component carriers f1 and f2, that the component carrier f1 is
set as a primary, and that a femto base station is installed on the
component carrier f2. In the first embodiment, the need for a
search and quality measurement for a neighboring cell is judged by
using as the reception quality the reception strength of the
component carrier f1 set as the primary. In this case, a
communication terminal may exist near the femto base station on the
component carrier f2 even when the quality of the component carrier
f1 is sufficient. The communication terminal does not perform a
search and quality measurement for a neighboring cell, therefore
cannot detect the presence of the femto base station, and may
suffer interference from the femto base station or may cause
interference to a communication terminal connected to the femto
base station. This problem may not be solved even by using as a
search threshold value the reception quality based on the reception
strength of the component carrier f2. This is because there may be
interference from the femto base station even if the reception
strength of a serving cell on the component carrier f2 is
sufficiently high. A solution to this may be the use of
interference-considered reception quality as shown in FIG. 32. RSRQ
(Reference Signal Received Quality) described in Non-patent
document 3 is the reception quality that takes into account not
only the reception strength but also interference. Thus, an
operation of making a comparison by using S-measure_RSRQ for each
component carrier is defined in addition to the operation described
in the first embodiment, in which a comparison is made by using
S-measure_RSRP based on RSRP for a primary component carrier. That
is, referring to the example in FIG. 32, the primary component
carrier frequency 1 is compared to the S-measure_RSRP and, when the
quality of the component carrier f1 becomes worse than the
S-measure_RSRP, all the configured search and measurement processes
are started as in the first embodiment. In addition, the quality of
the component carriers f1 and f2 is compared to the S-measure_RSRQ
and, when the quality of the component carrier f2 becomes worse
than the S-measure_RSRQ, the configured search and measurement for
a neighboring cell are started on the component carrier f2. This
allows the communication terminal 5 to reliably detect a femto base
station when there is one as shown in FIG. 31.
[0179] While a case is shown in FIG. 32 where the RSRQ of the
component carrier f2 becomes worse first, there may be a case where
the RSRQ of the component carrier f1 becomes worse first to be
worse than the S-measure_RSRQ. In such a case, it is also possible
that a search and measurement for a neighboring cell is started on
the component carrier f1 and not on the component carrier f2.
Conversely, all the configured neighboring cell search and
measurement processes can also be performed if the quality of the
primary component carrier becomes worse than either the
S-measure_RSRP or the S-measure_RSRQ.
[0180] This S-measure_RSRQ is required only when there is a femto
base station or the like on the network side and its interference
to a communication terminal cannot be estimated based on a primary
component carrier. For this reason, there may be an operation that
does not use S-measure_RSRQ. The operation in that case may be
according to the first embodiment not with S-measure_RSRQ being
transmitted but only with S-measure_RSRP. In a case where component
carriers to install femto base stations on are limited, it is also
conceivable to compare only such component carriers to
S-measure_RSRQ. One way to achieve this may be that a base station
notifies a communication terminal of component carriers to be
compared to S-measure_RSRQ.
[0181] FIGS. 33 and 34 show a block diagram and a flowchart,
respectively, of the communication terminal 5 for achieving the
above operation. Differences with the above-described embodiments
will be described below with reference to FIG. 33 first.
[0182] An RSRQ comparator 23 compares a quality measurement result
for each component carrier to a search threshold value for RSRQ
passed from the measurement configuration unit 12, and determines
whether to start a cell search or not for each component carrier.
The RSRQ comparator 23 notifies the cell search unit 22 of the
determination result. If this operation is to be used only for
certain component carriers here, the measurement configuration unit
12 specifies the certain component carriers.
[0183] The cell search unit 22 uses both comparison results
received from the comparator 16 and received from the RSRQ
comparator 23 to determine whether or not to perform a cell search.
If the cell search unit 22 determines to perform a cell search, it
does so according to the details configured by the measurement
configuration unit 12 and performs quality measurement for a
detected cell. The cell search unit 22 sends the measurement result
to the measurement result judging unit 18. An operation of the cell
search unit 22 for determining whether or not to perform a cell
search is shown in FIG. 34.
[0184] FIG. 34 shows an operation of the communication terminal 5.
A description will be given below of an operation of the
communication terminal 5 for determining whether or not to perform
a cell search, centering on differences with the above-described
embodiments. The measurement configuration unit 12 of the
communication terminal 5 receives a measurement configuration
transmitted from the base station 30 and sets the configuration
values (S10), and the primary carrier determination unit 13
determines a primary component carrier to be compared to a search
threshold value (S12); the operation is so far the same as that in
the first embodiment. The communication terminal 5 then judges
whether a measured value of the reception quality of the primary
component carrier is more than or equal to the search threshold
value or not (S13). This operation is almost the same as step S14
shown in FIG. 3, but is different therefrom in that the operation
goes on to step S15 if the judgment result is "Yes." In step S15,
the communication terminal 5 checks whether there is any component
carrier whose quality is less than or equal to the search threshold
value or not. Not RSRP, which is used in step S13, but RSRQ is used
here for the comparison to the search threshold value. If there is
a component carrier whose quality is less than or equal to the
search threshold value in this step, a neighboring cell search and
neighboring cell measurement are performed on the component carrier
concerned (S17).
[0185] The embodiment allows a terminal to detect an interfering
cell even in circumstances such as those shown in FIG. 31, and to
perform a process, for example, to stop the use of the component
carrier f2. This can realize an efficient carrier aggregation.
[0186] The concept of frequency band may be introduced into the
embodiment. Specifically, in a case where there are component
carriers f2 and f3 in the same frequency band (e.g. 800 MHz band)
and the two component carriers are used, if the quality (RSRQ in
this case) of either one of the component carriers falls below a
search threshold value (S-measure_RSRQ), a cell search may be
performed on both component carriers f2 and f3 in the same
frequency band. In addition, if there is another component carrier
f4 that is not currently used in the same frequency band but is in
the measurement configuration, the measurement for the component
carrier f4 may also be started.
[0187] While there have been described what are at present
considered to be preferred embodiments of the invention, various
modifications and variations may be made thereto, and it is
intended that appended claims cover all such modifications and
variations as fall within the true spirit and scope of the
invention.
INDUSTRIAL APPLICABILITY
[0188] The invention has an advantage of allowing even a
communication terminal supporting carrier aggregation to
appropriately start a cell search, and is useful as a communication
terminal, a base station, and the like that support carrier
aggregation.
DESCRIPTION OF THE SYMBOLS
[0189] 1-4: Communication terminal [0190] 11: Receiver [0191] 12:
Measurement configuration unit [0192] 13: Primary carrier
determination unit [0193] 14: Primary carrier storage unit [0194]
15: Quality measurement unit [0195] 16: Comparator [0196] 16a:
Primary comparator [0197] 16b: Secondary comparator [0198] 17: Cell
search unit [0199] 18: Measurement result judging unit [0200] 19:
Transmitter [0201] 20: Reception mode detector [0202] 30: Base
station [0203] 31: Terminal information manager [0204] 32:
Aggregation determination unit [0205] 33: Primary determination
unit [0206] 34: Configuration determination unit [0207] 35:
Transmitter
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